I don't think I'd ever use it in conversation, polite or impolite. There was however a game show in the UK called Catchword (early nineties?) where you had to make the longest word you could from a given set of letters. This particular F-word came up all the time.

It would be impolite to verbalize that word, because it is difficult to say without spraying spittle on nearby listeners--both while actually saying it, and then immediately afterward when you are snorting trying not to laugh.